JUnit assertTrue with Message

In this tutorial, we will see how to pass the message to JUnit assertTrue() static method and verify the supplied conditions are true.

Create Book Class

package junit5.bookstore.model;

public class Book {
	
	private String bookId;
	private String title;
	private String publisher;
	
	public Book(String bookId, String title, String publisher) {
		this.bookId = bookId;
		this.title = title;
		this.publisher = publisher;
	}

	public String getBookId() {
		return bookId;
	}

	public void setBookId(String bookId) {
		this.bookId = bookId;
	}

	public String getTitle() {
		return title;
	}

	public void setTitle(String title) {
		this.title = title;
	}

	public String getPublisher() {
		return publisher;
	}

	public void setPublisher(String publisher) {
		this.publisher = publisher;
	}
	
}

Create BookService Class

package junit5.bookstore.service;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import junit5.bookstore.model.Book;

public class BookService {
	
	private List<Book> listOfBooks = new ArrayList<>();
	
	public void addBook(Book book) {
		listOfBooks.add(book);
	}	
	
	public List<Book> books(){
		return Collections.unmodifiableList(listOfBooks);
	}
	
	public Book getBookById(String bookId) {
		for(Book book : listOfBooks) {
			if(bookId.equals(book.getBookId())) {
				return book;
			}
		}
		return null;
	}
	
	public String[] getBookIdsByPublisher(String publisher) {
		List<String> bookIds = new ArrayList<>();
		for(Book book : listOfBooks) {
			if(publisher.equals(book.getPublisher())) {
				bookIds.add(book.getBookId());
			}
		}
		return bookIds.toArray(new String[bookIds.size()]);
	}
	
	public List<String> getBookTitlesByPublisher(String publisher) {
		List<String> bookTitles = new ArrayList<>();
		for(Book book : listOfBooks) {
			if(publisher.equals(book.getPublisher())) {
				bookTitles.add(book.getTitle());
			}
		}
		return bookTitles;
	}
}

Write JUnit test to use assertTrue() method with Message

The below Java program demonstrates the usage of all overloaded assertTrue() static methods:

package junit5.assertions.assertTrue;

import static org.junit.jupiter.api.Assertions.assertTrue;

import java.util.List;

import org.junit.jupiter.api.Test;

import junit5.bookstore.model.Book;
import junit5.bookstore.service.BookService;

public class AssertTrueDemo {
	
	@Test
	public void assertTrueWithMessage() {
		BookService bookService = new BookService();

		List<Book> listOfBooks = bookService.books();
		
		assertTrue(listOfBooks.isEmpty(), "List of books is not empty!");
		
	}
	
	@Test
	public void assertTrueWithBooleanSupplierAndMessage() {
		BookService bookService = new BookService();

		List<Book> listOfBooks = bookService.books();
		
		assertTrue(() -> listOfBooks.isEmpty(), "List of books is not empty!");
		
	}
	
	@Test
	public void assertTrueWithMessageSupplier() {
		BookService bookService = new BookService();

		List<Book> listOfBooks = bookService.books();
		
		assertTrue(listOfBooks.isEmpty(), () -> "List of books is not empty!");
		
	}
	
	@Test
	public void assertTrueWithBooleanSupplierAndMessageSupplier() {
		BookService bookService = new BookService();
		
		Book headFirstJavaBook = new Book("1", "Head First Java", "Wrox");

		List<Book> listOfBooks = bookService.books();
		
		assertTrue(() -> listOfBooks.isEmpty(), () -> "List of books is not empty!");
	}
}

Run JUnit test Class

Run the JUnit test class to execute all the JUnit test cases and here is the output:


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